The three domains of life are Bacteria, Archaea, and Eukarya. This system groups all living organisms based on differences in cell structure, genetic material, and evolutionary ancestry. It allows scientists to classify species more accurately and study biodiversity from a molecular perspective. These domains form the highest level in biological taxonomy.

The system provides a global framework to categorize life. Unlike older systems, it uses molecular data—especially ribosomal RNA—to trace evolutionary lineages. Because of this, it reveals deeper relationships among organisms. It also helps biologists compare traits across distant species, supporting studies in genetics, ecology, and medicine.

Archaea and Bacteria both lack a nucleus, but Archaea have distinct membrane lipids and unique enzymes. Their genes also resemble those of Eukaryotes more than Bacteria. Furthermore, Archaea often thrive in harsh environments like acidic springs, deep-sea vents, and salty lakes—conditions most Bacteria cannot tolerate.

All complex, multicellular organisms—including humans, animals, plants, fungi, and protists—belong to the Eukaryadomain. These organisms have membrane-bound organelles, such as mitochondria and a defined nucleus. Eukaryotes can be unicellular or multicellular, and they form the most diverse and specialized domain in the tree of life.

In 1990, Carl Woese, an American microbiologist, introduced the three-domain system using ribosomal RNA sequencing. His work revealed that Archaea were genetically distinct from Bacteria. As a result, the new system replaced older two-kingdom or five-kingdom models and revolutionized how scientists study taxonomy and biodiversity.